This application relates generally to gas turbine engines and, more particularly, to gas turbine engine compressors.
A gas turbine engine typically includes a multi-stage axial compressor, a combustor, and a turbine. Airflow entering the compressor is compressed and directed to the combustor where it is mixed with fuel and ignited, producing hot combustion gases used to drive the turbine. As a result of the hot combustion gases entering the turbine, typically compressor air is channeled through a turbine cooling circuit and used to cool the turbine.
Compressor bleed air is often used as a source of cooling air for the turbine cooling circuit. However, extracting cooling air from the compressor may affect overall gas turbine engine performance. To minimize a reduction in engine performance, the cooling air is typically extracted from the lowest compressor stage that has a sufficient pressure for the turbine. Generally, because the temperature of air flowing through the compressor increases at each stage of the compressor, utilizing cooling air from the lowest allowable compressor stage results in a lower engine performance decrement as a result of such a cooling air extraction. Furthermore, the turbine is cooled more effectively when the cooling air is extracted from a source having a lower temperature. However, in gas turbine engines including radial outflow compressors or centrifugal compressors, cooling air is typically extracted at an inlet and/or exit of the centrifugal compressor. Cooling air extraction from the exit of the centrifugal compressor is often at a higher pressure level than needed for turbine cooling. An associated engine performance loss results from utilizing cooling air at such an excessive pressure level because additional work was done to compress such air and further because such air is at a higher temperature level. As a result, overall engine performance is affected and the turbine is cooled ineffectively.
In an exemplary embodiment, a gas turbine engine includes a compressor rotor assembly which effectively directs air downstream at a sufficient pressure and temperature to a downstream turbine for cooling. The compressor assembly includes a centrifugal compressor including an impeller, an impeller shroud/casing, and a cooling circuit. The centrifugal compressor includes an inlet, an exit, and a flowpath extending therebetween and defined by the rotating impeller and the non-rotating impeller shroud/casing. The impeller shroud includes a first opening that is positioned between the centrifugal compressor inlet and exit. The cooling circuit extends between the compressor and the turbine and is in flow communication with the impeller shroud opening.
In operation, compressor bleed air is extracted from the centrifugal compressor through the first opening. The air is channeled to the turbine and a portion of the air is directed radially inward to cool a shroud covering a portion of the turbine and a portion is directed upstream to cool a disk of the turbine. The cooling circuit extracts cooling air from the compressor at a location which provides cooling air at a temperature which effectively cools the turbine and at a pressure greater than a static pressure level in those regions cooled within the turbine by the cooling circuit. As a result, the turbine is effectively cooled to improve mechanical capability and durability of the turbine.